There are only a few reports in the literature of the occurrence of murine neoplasms of B lymphocytes with immunoglobulin on the cell surfaces and there are no reports where the cells were cultured and remained positive. Spontaneous tumors that arise in old BALB/c mice have M, A, G or an undetermined type of immunoglobulin on the tumor cell surfaces and the cells of some tumors remain positive in culture. The purpose of this study is to characterize the behavior of these tumors in transplant and to establish more tumors in transplant in order to obtain for future use more of the relatively rare A and G types of tumors.